This invention relates to an electric shutter operating circuit for use in a TTL single lens reflex camera.
As is well known in the art, since in the TTL single lens reflex camera, the intensity of the light from the field or an object to be photographed and passing through the lens system is measured, it is impossible to make such measurement at the time of photographing. For this reason, in an electric shutter operating circuit for use in the TTL single lens reflex camera it is necessary to provide a special circuit that memorizes the value of the measured light before commencing photographing. Although various types of practically applicable special circuits have been proposed, a circuit utilizing a negative feedback circuit has been deemed satisfactory because it can operate stably. However, a prior art specific circuit generally comprises a balanced circuit incorporating a differential amplifier circuit, or a circuit including means for logarithmically compressing and inserting information, so that such circuit has a tendency to become unstable. For this reason, it is advantageous to provide a negative feedback circuit as has been pointed out hereinabove. Several types of electric shutter operating circuits provided with negative feedback circuits have already been announced but in the operating circuit of this type it is necessary to use high grade technical skills for inserting compensating information regarding the opening of the iris diaphragm, the photosensitivity of the film used, etc. If such skills were not relied upon, even when information corrections are made these corrections would be automatically cancelled.